The paper firstly presents the features of video image, the model of noise, the common method of image-enhancement. And it analyses the features of image including of the small target, the means of SNR. At the base of this model, the high-pass filtering in spatial domain is used in the design. The simulation results proves that this method is effective with a useful SNR gain at the same time of having a good resolution in irregular information. For FPGA is used in the design of the preprocessing circle, there described the structures、features and applications of 4000 serial FPGA of Xilinx as a example of FPGA-one of the power and wide used members of programmable ASIC. The modern designing technique of circuit and system and programmable integrated circuit was introduced. The high-pass filtering circle was finished with FPGA. Then the one applications of FPGA in image processing system was presented. The preprocessing circuit was analyzed at first and then the way to solve the problem、FPGA implementation and the result of circuit test were presented; At the end the future of application of FPGA in image processing system was pointed out.